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The ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago. We know this because the orthocerids were the first known representatives of the neocephalopoda, [ 40 ] were ultimately the ancestors of ammonoids and ...
Good evidence exists for the appearance of gastropods, cephalopods and bivalves in the Cambrian period .However, the evolutionary history both of the emergence of molluscs from the ancestral group Lophotrochozoa, and of their diversification into the well-known living and fossil forms, is still vigorously debated.
Orthocerida, also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods that lived from the Early Ordovician) possibly to the Late Triassic 1] A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous 2] and the Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed.
Antarcticeras is an extinct genus of enigmatic cephalopod from the Eocene of Antarctica.It contains a single species, A. nordenskjoeldi.It is either considered the last of the "orthocone"-type cephalopods, the only member of its subclass Paracoleoidea & a descendant of the orthoceratids, and a remarkable example of convergent evolution with coleoid cephalopods, or an oegospid squid and a ...
Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silurian. Their shells were variable in form.
The other three unite related orders which share a common ancestor and form a branch of the nautiloid taxonomic tree: Plectronoceratoidea, which consists mostly of small Cambrian forms that include the ancestors of subsequent stocks; Orthoceratoidea, which unites different primarily orthoconic orders (including the ancestors for Bacritida and ...
Endoceras (Ancient Greek for "inner horn") is an extinct genus of large, straight shelled cephalopods that gives its name to the Nautiloid order Endocerida. The genus lived during the middle and upper Ordovician 470 to 443 million years ago. The cross section in the mature portion is slightly wider than high, but is narrower laterally in the young.
Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea.They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family Nautilidae). [1]